2 Layout and Use of Signals
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Part 6 Section 2 LAYOUT OF SIGNALS Issued May 1995 2 Layout and Use of Signals 2.1 General frame is shown between the signalman and the track. Locating the frame in this position has an Signals are provided to control the movement of effect on the numbering of the equipment con- trains and to inform the driver whether it is safe trolled by the box. to proceed. Their location is dictated largely by the track layout, the relevant Government Department’s minimum requirements and, to 2.1.2 Lever numbering some extent, by the frequency of train movements. Coupled with this are the variations in practice The levers in a frame are arranged in a straight that occurred from company to company. At one line and numbered consecutively with number 1 end of the scale there were companies that provid- always on the signalman’s left as he faces the ed signals for every conceivable movement while frame. The normal position of the levers is back in others only used the bare minimum required by the frame and when a lever is pulled it is said to routine work. When a special movement was be reversed. As far as possible the layout number- required, companies supplemented the fixed sig- ing is arranged so that, for the commonest train nals with oral or written instructions and hand movements, the levers are pulled in numerical signals. order. Modellers basing their layouts on prototype The normal practice is to number the levers in locations can, with a little research, find out the the same order that the equipment controlled ‘lies positions and types of signal used including on the ground’. In Figure 2-1, down line trains changes that may have occurred over the years. approach from the left, hence the down line signals Where the layout is a ‘might have been’ the follow- occupy the low numbers. Similarly the up line sig- ing notes can give initial guidance to correct signal nals occupy the high numbers. The crossovers and location. However, for the layout to be fully their associated ground signals are located in the authentic it is necessary to study the practices of middle of the frame and provide a physical separa- the company being portrayed. Luckily, there is a tion between the two sets of running signal levers. considerable amount of information available in In addition to their numbers, levers are also railway literature and from specialist societies, identified by their colours which indicate the par- particularly the Signalling Record Society. ticular function that they perform. The standard colours are:- Distant signals Yellow 2.1.1 Signal box interior layout Stop signals Red When a lever frame is fixed in a box there are two Points Black positions that it can occupy: Point locks Blue • With the signalman facing the running lines so Detonator Placers Black with White chevrons that he can see the points and signals while Spares White operating the levers. This has a disadvantage in that the signal levers, track diagram, block instruments, etc. tend to obstruct his view. In 2.1.3 Facing point locks and fouling bars addition, he only has access to the windows at either end of the frame for giving instructions Facing points on running lines carrying passenger to drivers or shunters. traffic are required to be fitted with facing point locks. The lock mechanism consists of a bar fitted • With the signalman having his back to the run- between the point blades that has either one or ning lines so that by turning round he has an two holes in it. Where passenger traffic used only uninterrupted view and access to all windows one of the facing roads and only non-passenger overlooking the line. traffic used the other road, it was the practice to There are no hard and fast rules but the latter provide a one-hole lock bar. However, it has now method was more often adopted when planning become general practice to provide a two-hole lock new frames in early BR days. Where signal boxes bar locking facing points both normal and reverse, are shown on track diagrams their orientation is regardless of traffic considerations. A sliding bolt, indicated by representing the frame by a thick line connected to a locking lever in the signal box, fits and the signalman by a dot. In Figure 2-1 the into the holes locking the points. In modern prac- Compiled by A. Garraway, J. R. Hadwin, D. Strivens, M. H. Walshaw. 6 - 2 - 1 Drawings devised by K. Sheale Artwork by Kensington Graphics tice when a facing point lock lever is normal in the provides an indication in addition to, or in place of, frame, the points are unbolted and free to be track circuiting. moved. When the lever is reversed the bolt is inserted and the points are locked. To reverse a set of facing points, the signalman 2.2 Typical Through Station first restores the locking lever to normal to unbolt Layouts the points. He then reverses the points and revers- es the locking lever. This inserts the bolt into the 2.2.1 Semaphore signalling at a through second hole in the stretcher bar locking the point station in the reversed position. To prevent points being moved under a train, Figure 2-1 shows the mechanical signalling that mechanically worked points are fitted with a foul- might be planned for a through station with two ing bar. This consists of a bar longer than the main crossovers and a siding connection. The sig- longest vehicle wheelbase (usually some 16m, or nals have been numbered and their functions 50ft, in length) which lies alongside the inside could be described as follows: edge of one of the running rails and is connected to 1. Down distant the facing point lock mechanism. Unbolting a fac- 2. Down home ing point lock causes the fouling bar to rise into 3. Down starting the flangeway. Should a train be passing, the foul- 4. Down advanced starting ing bar would be prevented from rising and, in 5. Call on to down platform turn, prevent the bolt from being withdrawn and 6. Shunt ahead down line the points moved. In modern practice, particularly 7. Shunt, up line to down platform with the advent of long modern coaching stock, the 8. Crossover, up line to down platform fouling bar has been replaced by electrical locking 9. Shunt, down platform to up line using the track circuits. 10. Shunt, up platform to down line 11. Crossover, up platform to down line 12. Shunt, down line to up platform 2.1.4 Electric depression bar 13. Shunt, down sidings to down line 14. Crossover, down sidings exit This device consists of a bar which lies in the 15. Shunt, down line to down sidings flangeway level with the running rails. It is fitted 16. Call on to up platform with electrical contacts which are activated when 17. Up advanced starting the bar is depressed by the weight of a locomotive 18. Up starting or other vehicle. It is found at the end of bay plat- 19. Up home forms and is used to remind the signalman of the 20. Up distant presence of a locomotive or vehicle standing there. It is often provided where, due to deposits on the Note 1: The shunt ahead signal (6) only needs to rails, the track circuiting is erratic in operation. It be provided if the distance between the siding points and the advanced starter (4) 13 Yellow Headshunt 14 1 5 2 3 6 4 Platform 14 Down 8 11 7 10 9 12 15 Up 8 11 Platform 17 18 19 16 20 Signal Box FIGURE 2-1 Typical Through Station with Semaphore Signalling. 6 - 2 - 2 Part 6 Section 2 LAYOUT OF SIGNALS Issued May 1995 is less than the normal length of train tant signal as a separate entity has virtually dis- that uses the siding. appeared. (Section 1.7 covers these changes). Note 2: If a train standing on the down line in the The introduction of three and four aspect sig- rear of advanced starter (4) was regularly nalling using automatic block working would often required to back into the down platform require the new signals to be located in different as far as ground signal (9), a third ground positions to the semaphores that they replaced. signal, in addition to (12) and (15), would These changes occurred where the new block sec- be needed to cover this movement. tions differed in length and/or to improve signal However, some railways, notably the SR sighting for the drivers benefit. In addition, many and the MR (prior to 1906), used a single of the subsidiary signals have been eliminated, for ground signal to cover all three routes on example in some areas the main signal is used to the principle that the driver knew where control Shunt Ahead movements. he wished to go and could see the lie of A variation that has been used for the Shunt the points. Again, company practice needs Ahead and Calling On signals is shown in the to be checked. drawing. In place of the single yellow or the two diagonal white lights described in Section 1.9, Note 3: Although not shown in the figure, a two some areas make use of a modified standard colour aspect green /yellow colour light distant light ground signal bracketed out from the post was sometimes used (from the 30’s to below the main signal. The normal aspect is with date) to replace a semaphore distant all lamps out.